II. Classification of Upland Cotton
A. Instrument Determinations
Measurements for the following quality factors are performed by high volume, precision instruments, commonly referred to as "HVI" classification.
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Fiber Length
Fiber length is the average length of the longer one-half of the fibers (upper half mean length). It is reported in both 100ths and 32nds of an inch (see conversion chart below). It is measured by passing a "beard" of parallel fibers through a sensing point. The beard is formed when fibers from a sample of cotton are grasped by a clamp, then combed and brushed to straighten and parallel the fibers.
Fiber length is largely determined by variety, but the cotton plant's exposure to extreme temperatures, water stress, or nutrient deficiencies may shorten the length. Excessive cleaning and/or drying at the gin may also result in shorter fiber length. Fiber length affects yarn strength, yarn evenness, and the efficiency of the spinning process. The fineness of the yarn which can be successfully produced from given fibers is also influenced by the length of the fiber.
| Upland Length Conversion Chart |
| Inches |
32nds |
Inches |
32nds |
| 0.79 & shorter |
24 |
1.11 - 1.13 |
36 |
| 0.80 - .85 |
26 |
1.14 - 1.17 |
37 |
| 0.86 - .89 |
28 |
1.18 - 1.20 |
38 |
| 0.90 - .92 |
29 |
1.21 - 1.23 |
39 |
| 0.93 - .95 |
30 |
1.24 - 1.26 |
40 |
| 0.96 - .98 |
31 |
1.27 - 1.29 |
41 |
| 0.99 -1.01 |
32 |
1.30 - 1.32 |
42 |
| 1.02 -1.04 |
33 |
1.33 - 1.35 |
43 |
| 1.05 -1.07 |
34 |
1.36 & longer |
44 & longer |
| 1.08 -1.10 |
35 |
|
|
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Length Uniformity
Length uniformity is the ratio between the mean length and the upper half mean length of the fibers and is expressed as a percentage. If all of the fibers in the bale were of the same length, the mean length and the upper half mean length would be the same, and the uniformity index would be 100. However, there is a natural variation in the length of cotton fibers, so length uniformity will always be less than 100. The following table can be used as a guide in interpreting length uniformity measurements.
Length uniformity affects yarn evenness and strength, and the efficiency of the spinning process. It is also related to short fiber content (fiber shorter than one half inch) . Cotton with a low uniformity index is likely to have a high percentage of short fibers. Such cotton may be difficult to process and is likely to produce low-quality yarn.
| Degree of Uniformity |
HVI Length Uniformity Index (Percent) |
| Very High |
Above 85 |
| High |
83-85 |
| Intermediate |
80 - 82 |
| Low |
77 - 79 |
| Very Low |
Below 77 |
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The Classification of Cotton
